JP5642459B2 - Photocatalyst electrode, hydrogen generator, and hydrogen generation method - Google Patents
Photocatalyst electrode, hydrogen generator, and hydrogen generation method Download PDFInfo
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- 239000001257 hydrogen Substances 0.000 title claims description 104
- 229910052739 hydrogen Inorganic materials 0.000 title claims description 104
- 238000000034 method Methods 0.000 title claims description 8
- 230000001699 photocatalysis Effects 0.000 claims description 38
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 34
- 229910002367 SrTiO Inorganic materials 0.000 claims description 26
- 239000004065 semiconductor Substances 0.000 claims description 23
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- 239000010948 rhodium Substances 0.000 description 45
- 238000006722 reduction reaction Methods 0.000 description 18
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 14
- 238000005868 electrolysis reaction Methods 0.000 description 13
- 238000005259 measurement Methods 0.000 description 13
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 9
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- 238000004519 manufacturing process Methods 0.000 description 9
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 8
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- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
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- Inorganic Compounds Of Heavy Metals (AREA)
- Catalysts (AREA)
- Electrodes For Compound Or Non-Metal Manufacture (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
Description
本発明は、光触媒電極および当該光触媒電極を用いた水素生成装置、並びに当該水素生成装置によって水素を生成する方法に関する。 The present invention relates to a photocatalyst electrode, a hydrogen generator using the photocatalyst electrode, and a method for generating hydrogen by the hydrogen generator.
地球規模でのエネルギー・環境問題の観点から、太陽光エネルギーを利用することができる科学技術の開発が切望されている。さらに、太陽光エネルギーを化学エネルギーに転換する、すなわち太陽光エネルギーを利用して燃料を製造する技術が注目されている。このようなソーラーフュエルを生成することができる方法として、半導体特性を有する光触媒電極を用いた水の分解がある。
光触媒電極の材料は非常に限られており、例えば、ＴｉＯ2 （非特許文献１参照。）、ＳｒＴｉＯ3 （チタン酸ストロンチウム）（非特許文献２〜４参照。）、ＫＴａＯ3 （非特許文献５参照。）、ＷＯ3 （非特許文献６参照。）、Ｆｅ2 Ｏ3 （非特許文献７参照。）などが挙げられる。
From the viewpoint of global energy and environmental problems, the development of science and technology that can use solar energy is eagerly desired. Furthermore, technology that converts solar energy into chemical energy, that is, a fuel that uses solar energy, has attracted attention. As a method for producing such a solar fuel, there is decomposition of water using a photocatalytic electrode having semiconductor characteristics.
The material of the photocatalytic electrode is very limited. For example, TiO 2 (see Non-Patent Document 1), SrTiO 3 (Strontium Titanate) (see Non-Patent Documents 2 to 4), KTaO 3 (Non-Patent Document 5). And WO 3 (see Non-Patent Document 6), Fe 2 O 3 (see Non-Patent Document 7), and the like.
しかしながら、ＴｉＯ2 による光触媒電極を用いて水の分解を行う場合には、ＴｉＯ2 のバンドギャップが３．０ｅＶであるために紫外線しか利用することができず、光源として太陽を利用するときにその利用効率が極めて低いものとなる。さらに、外部バイアスの印加も不可欠である。また、ＳｒＴｉＯ3 やＫＴａＯ3 による光触媒電極を用いて水の分解を行う場合には、外部バイアスの印加は要さないものの、やはりＳｒＴｉＯ3 やＫＴａＯ3 のバンドギャップが広いために紫外光しか利用することができない。
また、ＷＯ3 やＦｅ2 Ｏ3 による光触媒電極を用いて水の分解を行う場合には、ＷＯ3 やＦｅ2 Ｏ3 のバンドギャップが比較的狭いために可視光を利用することができるが、外部バイアスの印加は不可欠である。
そして、これらの光触媒電極の材料は、すべてｎ型半導体特性を示すものである。すなわち、水の分解において、これらの光触媒電極表面上に酸素が生成され、白金などの対極表面上に水素が生成される。
However, in the case of performing the decomposition of water using a photocatalyst electrode by TiO 2 can not band gap of TiO 2 is only utilized UV in order to be 3.0 eV, that when utilizing solar as a light source The utilization efficiency is extremely low. In addition, the application of an external bias is essential. Further, when the decomposition of water using a photocatalyst electrode according SrTiO 3 or KTaO 3, although not requiring application of an external bias, also only ultraviolet light is utilized for the band gap of SrTiO 3 or KTaO 3 is wide I can't.
Further, when the decomposition of water using a photocatalyst electrode by WO 3 and Fe 2 O 3, which may be a band gap of WO 3 and Fe 2 O 3 is using visible light to a relatively narrow, Application of an external bias is essential.
All of these photocatalytic electrode materials exhibit n-type semiconductor characteristics. That is, in the decomposition of water, oxygen is generated on the surface of these photocatalytic electrodes, and hydrogen is generated on the surface of the counter electrode such as platinum.
これに対して、ｐ型半導体特性を示す材料による光触媒電極においては、当該光触媒電極の表面において水素が生成され、対極において酸素が生成される。このような特性を利用して、例えばｎ型半導体特性を示す光触媒電極と組み合わせて用いて効率よく水の分解を行うなどのために、ｐ型半導体特性を示す光触媒電極が求められている。このｐ型半導体特性を示す光触媒電極の開発は、水の分解の分野においてのみならず、エレクトロニクス、オプトエレクトロニクス、太陽電池などの分野においても、非常に重要な課題とされている。
ｐ型半導体特性を示す光触媒電極の材料としては、ＣａＦｅ2 Ｏ4 が報告されている（非特許文献８参照。）が、それ以外の材料はほとんどないのが現状である。
In contrast, in a photocatalytic electrode made of a material exhibiting p-type semiconductor characteristics, hydrogen is produced on the surface of the photocatalytic electrode and oxygen is produced on the counter electrode. A photocatalyst electrode exhibiting p-type semiconductor characteristics is required in order to efficiently decompose water by using such characteristics in combination with, for example, a photocatalyst electrode exhibiting n-type semiconductor characteristics. The development of this photocatalytic electrode exhibiting p-type semiconductor characteristics is regarded as a very important issue not only in the field of water decomposition but also in the fields of electronics, optoelectronics, solar cells and the like.
CaFe 2 O 4 has been reported as a photocatalytic electrode material exhibiting p-type semiconductor characteristics (see Non-Patent Document 8), but there are almost no other materials.
しかしながら、ＣａＦｅ2 Ｏ4 による光触媒電極を用いた場合も、やはり外部バイアスの印加が不可欠である。 However, even when a photocatalytic electrode made of CaFe 2 O 4 is used, it is essential to apply an external bias.
以上から理解されるように、外部バイアスを印加することなしに、かつ、可視光の照射下において水の分解をすることができる、ｐ型半導体特性を有する光触媒電極が求められている。 As can be understood from the above, there is a need for a photocatalytic electrode having p-type semiconductor properties that can decompose water without applying an external bias and under irradiation with visible light.
ところで、ＳｒＴｉＯ3 は、紫外光の照射下において水の分解に活性を示す光触媒である（非特許文献９参照。）。
そして、種々の遷移金属をドープしたＳｒＴｉＯ3 が可視光の照射下において犠牲試薬を含む水溶液から、水素または酸素生成反応に活性を示すことが報告されている（非特許文献１０、特許文献１参照。）。中でもＲｈ（ロジウム）がドープされたＳｒＴｉＯ3 は、可視光の照射下におけるメタノール水溶液からの水素生成反応に高い活性を示すことが知られており（特許文献１参照。）、さらに、このＲｈがドープされたＳｒＴｉＯ3 と、ＷＯ3 系（非特許文献１１参照。）、ＢｉＶＯ4 系（非特許文献１２参照。）およびＢｉ2 ＭｏＯ6 （非特許文献１３参照。）系などの酸素生成反応に活性を示す光触媒と、種々の電子伝達剤とを組み合わせたＺ−スキーム型光触媒が、可視光の照射下に水を分解することができることが報告されているものの（特許文献２参照。）、このＲｈがドープされたＳｒＴｉＯ3 は、一般的にはＳｒＴｉＯ3 に酸素欠陥ができるためにｎ型半導体特性を示す、すなわち紫外光の照射下においてアノード光電流が得られることが知られており、実際、非特許文献１４には、ＳｒＴｉＯ3 のＴｉサイトにＲｈなどの少量の遷移金属をドープした光触媒電極が、可視光の照射下においてアノード光電流が測定されること、すなわちｎ型半導体特性を示すことが報告されている。
By the way, SrTiO 3 is a photocatalyst that is active in the decomposition of water under irradiation of ultraviolet light (see Non-Patent Document 9).
And it has been reported that SrTiO 3 doped with various transition metals shows activity in hydrogen or oxygen generation reaction from an aqueous solution containing a sacrificial reagent under irradiation with visible light (see Non-Patent Document 10 and Patent Document 1). .) Among them, SrTiO 3 doped with Rh (rhodium) is known to exhibit high activity in hydrogen generation reaction from aqueous methanol solution under visible light irradiation (see Patent Document 1). Doped SrTiO 3 and oxygen generation reaction such as WO 3 system (see Non-Patent Document 11), BiVO 4 system (see Non-Patent Document 12) and Bi 2 MoO 6 (see Non-Patent Document 13) Although it has been reported that a Z-scheme type photocatalyst combining an active photocatalyst and various electron transfer agents can decompose water under irradiation with visible light (see Patent Document 2). SrTiO 3 which Rh is doped, an n-type semiconductor characteristics, i.e., the anode photocurrent under irradiation of ultraviolet light obtained in order to be oxygen defects in SrTiO 3 is generally Doo is known, in fact, Non-Patent Document 14, the photocatalyst electrode doped with small amounts of transition metals such as Rh on the Ti site of SrTiO 3 is measured anode photocurrent under the irradiation of visible light That is, it has been reported to exhibit n-type semiconductor characteristics.
本発明は、以上の事情に基づいてなされたものであって、その目的は、ｐ型半導体特性を示す光触媒電極を提供することにある。
本発明の他の目的は、水の理論分解電圧未満の外部バイアスの印加条件下において光触媒電極表面上に水素が生成される水素生成装置、特に、可視光の照射下において水素が生成される水素生成装置を提供することにある。
本発明のさらに他の目的は、水の理論分解電圧未満の外部バイアスの印加条件下において水素を生成する水素生成方法、特に、可視光の照射下において水素を生成する水素生成方法を提供することにある。
This invention is made | formed based on the above situation, The objective is to provide the photocatalyst electrode which shows a p-type semiconductor characteristic.
Another object of the present invention is to provide a hydrogen generator that generates hydrogen on the surface of the photocatalytic electrode under the application of an external bias that is less than the theoretical decomposition voltage of water, particularly hydrogen that generates hydrogen under irradiation with visible light. It is to provide a generation device.
Still another object of the present invention is to provide a hydrogen generation method that generates hydrogen under the application of an external bias less than the theoretical decomposition voltage of water, and particularly a hydrogen generation method that generates hydrogen under irradiation with visible light. It is in.
本発明の光触媒電極は、ＳｒＴｉＯ3 のＴｉサイトにＲｈをドープしてなる光触媒を有し、
Ｒｈのドープ量が、当該ＳｒＴｉＯ 3 中においてＴｉ原子とＲｈ原子の合計を１００モル％としたときに、４〜１０モル％であり、ｐ型半導体特性を示すことを特徴とする。
本発明の光触媒電極においては、Ｒｈのドープ量が、前記ＳｒＴｉＯ 3 中においてＴｉ原子とＲｈ原子の合計を１００モル％としたときに、４〜７モル％であることが好ましい。
本発明の光触媒電極においては、前記光触媒が、水素還元処理されてなるものであることが好ましい。
The photocatalytic electrode of the present invention has a photocatalyst formed by doping Rh with Ti site of SrTiO 3 ,
The doping amount of Rh is 4 to 10 mol% when the total of Ti atoms and Rh atoms is 100 mol% in the SrTiO 3 , and exhibits p-type semiconductor characteristics.
In the photocatalytic electrode of the present invention, the doping amount of Rh is preferably 4 to 7 mol% when the total of Ti atoms and Rh atoms is 100 mol% in the SrTiO 3 .
In the photocatalyst electrode of the present invention, it is preferable that the photocatalyst is subjected to hydrogen reduction treatment.
本発明の水素生成装置は、上記の光触媒電極と対極とを有してなり、
前記光触媒電極と前記対極との間に外部バイアスを印加することなくまたは水の理論分解電圧未満の外部バイアスを印加すると共に、前記光触媒電極の光触媒に光を照射することにより、水が分解されて当該光触媒電極表面上に水素が生成されることを特徴とする。
The hydrogen generator of the present invention comprises the above-mentioned photocatalytic electrode and a counter electrode,
Water is decomposed by applying light to the photocatalyst of the photocatalyst electrode without applying an external bias between the photocatalyst electrode and the counter electrode or by applying an external bias lower than the theoretical decomposition voltage of water. Hydrogen is generated on the surface of the photocatalyst electrode.
本発明に水素生成装置においては、光触媒に照射される光が、可視光または太陽光とすることができる。 In the hydrogen generator of the present invention, the light applied to the photocatalyst can be visible light or sunlight.
本発明の水素生成方法は、上記の水素生成装置によって水素を生成することを特徴とする。 The hydrogen generation method of the present invention is characterized in that hydrogen is generated by the hydrogen generation apparatus described above.
本発明の光触媒電極によれば、当該光触媒電極がＳｒＴｉＯ3 のＴｉサイトに特定量のＲｈをドープしてなる光触媒を有するものであるために、ｐ型半導体特性を示す。
本発明の水素生成装置によれば、上記の光触媒電極を用いているために、当該光触媒電極の光触媒への光の照射下において、外部バイアスを印加することなくまたは水の理論分解電圧である１．２３Ｖ未満の外部バイアスの印加によって、水を分解して光触媒電極表面上に水素を生成させることができる。
According to the photocatalyst electrode of the present invention, since the photocatalyst electrode has a photocatalyst obtained by doping a Ti site of SrTiO 3 with a specific amount of Rh, p-type semiconductor characteristics are exhibited.
According to the hydrogen generator of the present invention, since the photocatalyst electrode is used, it is a theoretical decomposition voltage of water without applying an external bias or 1 under irradiation of light to the photocatalyst of the photocatalyst electrode. By applying an external bias of less than .23 V, water can be decomposed to generate hydrogen on the surface of the photocatalytic electrode.
以下、本発明について具体的に説明する。 Hereinafter, the present invention will be specifically described.
〔光触媒電極〕
本発明の光触媒電極は、ＳｒＴｉＯ3 のＴｉサイトにＲｈを４〜１０モル％ドープしてなる光触媒（以下、「特定の光触媒」ともいう。）を有し、ｐ型半導体特性を示すことを特徴とするものである。
ここに、「ＳｒＴｉＯ3 のＴｉサイトにＲｈを４〜１０モル％ドープしてなる」とは、ＳｒＴｉＯ3 中において、Ｔｉ原子とＲｈ原子の合計を１００モル％としたときに、Ｒｈ原子が４〜１０モル％存在することをいう。
[Photocatalytic electrode]
The photocatalytic electrode of the present invention has a photocatalyst (hereinafter also referred to as “specific photocatalyst”) obtained by doping 4 to 10 mol% of Rh at the Ti site of SrTiO 3 and exhibits p-type semiconductor characteristics. It is what.
Here, “the SrTiO 3 Ti site is doped with 4 to 10 mol% of Rh” means that, in SrTiO 3 , when the total amount of Ti atoms and Rh atoms is 100 mol%, Rh atoms are 4 -10 mol% is present.
Ｒｈのドープ量が上記の範囲にあることにより、光触媒電極が確実にｐ型半導体特性を示すものとなる。一方、Ｒｈのドープ量が４モル％未満である場合は、光触媒電極が十分なｐ型半導体特性を示すものとならないおそれがあり、また、Ｒｈのドープ量が１０モル％を超える場合は、ＳｒＴｉＯ3 の結晶構造中においてＲｈ原子をＴｉ原子に置き換えることのできるドープ限界を大きく逸脱するために、得られる光触媒がＳｒＲｈ2 Ｏ4 などの不純物を多量に含有するものとなって実用に適さないおそれがあり、また、得られる光触媒電極を用いた水素生成装置においてＲｈのドープ量に応じた量の水素を生成させることができない。 When the doping amount of Rh is in the above range, the photocatalytic electrode surely exhibits p-type semiconductor characteristics. On the other hand, when the doping amount of Rh is less than 4 mol%, the photocatalytic electrode may not exhibit sufficient p-type semiconductor characteristics, and when the doping amount of Rh exceeds 10 mol%, SrTiO In order to greatly deviate from the doping limit that can replace Rh atoms with Ti atoms in the crystal structure of 3 , the resulting photocatalyst may contain a large amount of impurities such as SrRh 2 O 4 and may not be suitable for practical use. In addition, in the hydrogen generator using the resulting photocatalytic electrode, it is not possible to generate hydrogen in an amount corresponding to the doping amount of Rh.
Ｒｈのドープ量は、４〜７モル％であることが好ましく、特に７モル％であることが好ましい。 The doping amount of Rh is preferably 4 to 7 mol%, particularly preferably 7 mol%.
〔光触媒の製造方法〕
このような光触媒電極を形成する特定の光触媒は、例えば、固相法によって合成することができる。
具体的には、例えば、少量のメタノールを用い、Ｓｒ源となるＳｒＣＯ3 、Ｔｉ源となるＴｉＯ2 、Ｒｈ源となるＲｈ2 Ｏ3 を、Ｓｒ原子、Ｔｉ原子およびＲｈ原子のモル比がＳｒ:Ｔｉ:Ｒｈ＝１:（１−ｘ）:ｘ（ｘ＝０．０４〜０．１）となるよう用いて、これらをアルミナ乳鉢で混合し、焼成処理することにより、粉末状の生成物として特定の光触媒を製造することができる。
Ｓｒ源となるＳｒＣＯ3 は、５〜１０モル％過剰に、すなわち上記のモル比がＳｒ:Ｔｉ:Ｒｈ＝１．０５:（１−ｘ）:ｘ〜１．１０：（１−ｘ）:ｘとなるよう使用することが好ましく、特に好ましくは７モル％過剰に使用することである。
Ｓｒ源となるＳｒＣＯ3 を過剰に使用する理由は、「日本化学会第８８春平年会予稿集」２００８，１Ｌ３−４２に示されるように、ＲｈをドープしたＳｒＴｉＯ3 について、Ｓｒ源となるＳｒＣＯ3 を量論比通りに使用した場合に比べ、Ｓｒ源となるＳｒＣＯ3 を７モル％過剰に使用して合成した場合に水素生成反応に係る光触媒活性が高くなるためである。なお、Ｓｒ源となるＳｒＣＯ3 を量論比通りに使用しても高い光触媒活性が得られない理由は、Ｓｒ源を量論比通りに使用しても固相法による合成においては多少なりともＳｒが偏在するために、Ｓｒ3 Ｔｉ2 Ｏ7 、Ｓｒ4 Ｔｉ3 Ｏ12などのＳｒが過剰な組成の不純物と、それに伴ってＳｒサイトに欠陥を有するＳｒＴｉＯ3 とが生成されてしまうためである。
[Production method of photocatalyst]
The specific photocatalyst forming such a photocatalytic electrode can be synthesized by, for example, a solid phase method.
Specifically, for example, using a small amount of methanol, SrCO 3 as a Sr source, TiO 2 as a Ti source, Rh 2 O 3 as a Rh source, and a molar ratio of Sr atoms, Ti atoms, and Rh atoms to Sr : Ti: Rh = 1: (1-x): x (x = 0.04 to 0.1), these are mixed in an alumina mortar and fired to obtain a powdered product As a specific photocatalyst can be produced.
SrCO 3 serving as the Sr source is in an excess of 5 to 10 mol%, that is, the above molar ratio is Sr: Ti: Rh = 1.05: (1-x): x to 1.10: (1-x): It is preferable to use it so that it will be x, and it is especially preferable to use it in excess of 7 mol%.
The reason for excessive use of SrCO 3 as a Sr source is that, as shown in “The Chemical Society of Japan 88th Spring Annual Meeting Proceedings” 2008, 1L3-42, for SrTiO 3 doped with Rh, SrCO as the Sr source. This is because the photocatalytic activity related to the hydrogen generation reaction is increased when SrCO 3 serving as the Sr source is used in an excess of 7 mol% compared to the case where 3 is used in a stoichiometric ratio. The reason why high photocatalytic activity cannot be obtained even when SrCO 3 serving as the Sr source is used according to the stoichiometric ratio is that, even if the Sr source is used according to the stoichiometric ratio, in the synthesis by the solid phase method, it is somewhat. Because Sr is unevenly distributed, impurities with an excessive Sr composition such as Sr 3 Ti 2 O 7 and Sr 4 Ti 3 O 12 and SrTiO 3 having defects at the Sr site are generated accordingly. is there.
〔水素還元処理〕
この光触媒電極は、これを形成する特定の光触媒が、水素還元処理されてなるものであることが好ましい。
特定の光触媒の水素還元処理は、具体的には、例えば特定の光触媒を石英管内に入れ、当該石英管内を水素ガスで置換した後に、加熱することにより行うことができる。
加熱温度は例えば２００〜５００℃、加熱時間は例えば１〜１０時間とされることが好ましい。
[Hydrogen reduction treatment]
The photocatalyst electrode is preferably obtained by hydrogen reduction treatment of a specific photocatalyst forming the photocatalyst electrode.
Specifically, the hydrogen reduction treatment of a specific photocatalyst can be performed, for example, by placing the specific photocatalyst in a quartz tube and replacing the quartz tube with hydrogen gas, followed by heating.
The heating temperature is preferably 200 to 500 ° C. and the heating time is preferably 1 to 10 hours, for example.
このような光触媒電極は、具体的には、例えば、図１に示されるように、特定の光触媒を含有する触媒ペーストを、ＩＴＯ透明電極２５の導電面２５Ａにおける光触媒部形成領域（図示せず）上に塗布し、次いで、大気中にて焼成処理をして光触媒部２１を形成した後、ＩＴＯ透明電極２５の導電面２５Ａにおける光触媒部２１を形成されていない領域にＧａ−Ｉｎ合金を塗布してオーミック接触部２６を形成し、そこに伸縮チューブ２３で被覆した銅線２４を銀ペーストで接着し、アラルダイト（登録商標）などのエポキシ系接着剤でＩＴＯ透明電極２５と銅線２４を接着し、最後に、光触媒部２１が形成されていないＩＴＯ透明電極２５の露出部分をアラルダイト（登録商標）で覆うことにより、得ることができる。
焼成処理の温度は例えば１００〜３００℃、焼成処理の時間は例えば１〜５時間とされることが好ましい。
Specifically, for example, as shown in FIG. 1, such a photocatalyst electrode is obtained by applying a catalyst paste containing a specific photocatalyst to a photocatalyst portion formation region (not shown) on the conductive surface 25 </ b> A of the ITO transparent electrode 25. Then, after applying the baking process in the atmosphere to form the photocatalyst portion 21, a Ga-In alloy is applied to the region of the conductive surface 25A of the ITO transparent electrode 25 where the photocatalyst portion 21 is not formed. The ohmic contact portion 26 is formed, and the copper wire 24 covered with the expansion tube 23 is adhered thereto with a silver paste, and the ITO transparent electrode 25 and the copper wire 24 are adhered with an epoxy adhesive such as Araldite (registered trademark). Finally, the exposed portion of the ITO transparent electrode 25 where the photocatalyst portion 21 is not formed can be obtained by covering with an Araldite (registered trademark).
It is preferable that the temperature of the baking treatment is, for example, 100 to 300 ° C., and the time of the baking treatment is, for example, 1 to 5 hours.
〔水素生成装置〕
本発明の水素生成装置は、上記の光触媒電極と対極とを有してなり、光触媒電極と前記対極との間に外部バイアスを印加することなく、または水の理論分解電圧である１．２３Ｖ未満の外部バイアスを印加すると共に、光触媒電極を形成する特定の光触媒に光を照射することにより、水が分解されて当該光触媒電極表面上に水素が生成されることを特徴とするものである。
[Hydrogen generator]
The hydrogen generator of the present invention has the photocatalyst electrode and a counter electrode, and does not apply an external bias between the photocatalyst electrode and the counter electrode, or is less than 1.23 V, which is the theoretical decomposition voltage of water. When an external bias is applied and light is applied to a specific photocatalyst forming the photocatalyst electrode, water is decomposed to generate hydrogen on the surface of the photocatalyst electrode.
具体的には、図２に示されるように、セル１０がイオン交換膜１２によって区画されることにより形成されたカソード室１３Ａおよびアノード室１３Ｂに、それぞれ、光触媒電極１５および対極１７が設けられると共に、当該光触媒電極１５および対極１７が電気的に接続されて構成される。
水の理論分解電圧未満の外部バイアスを印加するよう構成される場合は、光触媒電極１５と対極１７との間に、光触媒電極１５を陰極、対極１７を陽極として電圧を印加する直流電源よりなる電圧印加手段１９が設けられる。
Specifically, as shown in FIG. 2, a photocatalyst electrode 15 and a counter electrode 17 are provided in a cathode chamber 13A and an anode chamber 13B formed by partitioning the cell 10 with an ion exchange membrane 12, respectively. The photocatalytic electrode 15 and the counter electrode 17 are electrically connected.
When configured to apply an external bias less than the theoretical decomposition voltage of water, a voltage comprising a DC power source that applies a voltage between the photocatalyst electrode 15 and the counter electrode 17 with the photocatalyst electrode 15 as a cathode and the counter electrode 17 as an anode. Application means 19 is provided.
対極１７としては、例えば白金よりなるものを挙げることができ、また、ｎ型半導体特性を示す光触媒電極なども挙げることができる。
また、イオン交換膜１２としては、例えば「Ｎａｆｉｏｎ（登録商標）Ｒ１１７」（ＤｕＰｏｎｔ社製）などを用いることができる。
また、電圧印加手段１９としては、例えばポテンショスタット「ＨＺ−５０００」（北斗電工社製）などを用いることができる。
Examples of the counter electrode 17 include those made of platinum, and a photocatalytic electrode exhibiting n-type semiconductor characteristics.
As the ion exchange membrane 12, for example, “Nafion (registered trademark) R117” (manufactured by DuPont) or the like can be used.
Moreover, as the voltage application means 19, potentiostat "HZ-5000" (made by Hokuto Denko) etc. can be used, for example.
このような水素生成装置は、セル１０内に、光触媒電極１５および対極１７が共に浸漬されるよう、電解液Ｗとして水を充填すると共に、外部バイアスを印加する場合は印加しながら、光触媒電極１５を構成する特定の光触媒による光触媒部２１に光Ｌを照射することによって、光触媒電極１５が還元電極として作用して水が還元されてその表面上に水素が生成されると共に、対極１７が酸化電極として作用して水が酸化されてその表面上に酸素が生成され、これにより、水の分解が行われる。 Such a hydrogen generator fills water as the electrolyte W so that the photocatalyst electrode 15 and the counter electrode 17 are both immersed in the cell 10 and applies an external bias while applying the photocatalyst electrode 15. By irradiating light L to the photocatalyst portion 21 of the specific photocatalyst constituting the photocatalyst electrode 15 acts as a reduction electrode, water is reduced and hydrogen is generated on the surface, and the counter electrode 17 is an oxidation electrode. As a result, the water is oxidized and oxygen is generated on the surface thereof, whereby the water is decomposed.
特定の光触媒による光触媒部２１に照射される光としては、紫外光、可視光、太陽光などが挙げられる。
紫外光としては、例えば光源としてキセノンランプを用いて波長３００ｎｍ以下の波長範囲の光をカットした光が挙げられ、可視光としては、例えば光源としてキセノンランプを用いて波長４２０ｎｍ以下の波長範囲の光をカットした光が挙げられる。
特定の光触媒による光触媒部２１に照射される光としては、省エネルギーの観点から、可視光、太陽光が好ましく、特に太陽光が好ましい。
As light irradiated to the photocatalyst part 21 by a specific photocatalyst, ultraviolet light, visible light, sunlight, etc. are mentioned.
Examples of the ultraviolet light include light obtained by cutting light having a wavelength range of 300 nm or less using a xenon lamp as a light source, and examples of visible light include light having a wavelength range of 420 nm or less using a xenon lamp as a light source. The light which cuts.
As light irradiated to the photocatalyst part 21 by a specific photocatalyst, visible light and sunlight are preferable from a viewpoint of energy saving, and sunlight is particularly preferable.
分解する水は、水の酸化還元反応以外の反応を起こさず、物理的、化学的に安定で、ｐＨが中性付近であって、溶液の電気伝導性が良くなるために、Ｋ2 ＳＯ4 などを、０．０５〜０．２モル／Ｌ溶解させたものであってもよい。 The water to be decomposed does not cause any reaction other than the redox reaction of water, is physically and chemically stable, has a pH near neutral, and improves the electrical conductivity of the solution. Therefore, K 2 SO 4 Or the like may be dissolved in an amount of 0.05 to 0.2 mol / L.
以上のような水素生成装置によれば、ｐ型半導体特性を示す特定の光触媒によって形成された光触媒電極１５を用いているために、当該特定の光触媒による光触媒部２１への光の照射下において、外部バイアスを印加することなくまたは水の理論分解電圧である１．２３Ｖ未満の外部バイアスの印加によって、水を分解して光触媒電極１５の表面上に水素を生成させることができる。 According to the hydrogen generation apparatus as described above, since the photocatalyst electrode 15 formed by a specific photocatalyst exhibiting p-type semiconductor characteristics is used, Hydrogen can be generated on the surface of the photocatalytic electrode 15 by decomposing water without applying an external bias or by applying an external bias of less than 1.23 V, which is the theoretical decomposition voltage of water.
以上、本発明の実施形態について具体的に説明したが、本発明の実施形態は上記の例に限定されるものではなく、種々の変更を加えることができる。 As mentioned above, although embodiment of this invention was described concretely, embodiment of this invention is not limited to said example, A various change can be added.
以下、本発明の具体的な実施例について説明するが、本発明はこれらに限定されるものではない。 Hereinafter, specific examples of the present invention will be described, but the present invention is not limited thereto.
〔光触媒の調製例ａ〜ｄ、ｐ〜ｒ〕
ＲｈドープＳｒＴｉＯ3 を、固相法によって合成した。
具体的には、少量のメタノール（関東化学；９９、８％）を用い、ＳｒＣＯ3 （関東化学社製；９９．９％）、ＴｉＯ2 （添川理化学社製；９９．９％）、Ｒｈ2 Ｏ3 （和光純薬社製）を、Ｓｒ原子、Ｔｉ原子およびＲｈ原子のモル比がＳｒ:Ｔｉ:Ｒｈ＝１．０７:（１−ｘ）:ｘ（ｘ＝０〜０．１）となるよう用いて、これらをアルミナ乳鉢で混合した。次いで、９００℃で１時間仮焼成し、１１００℃で１０時間本焼成することにより、粉末状の生成物〔ａ〕〜〔ｄ〕、〔ｐ〕〜〔ｒ〕を得た。
なお、生成物〔ａ〕はｘ＝０．０４、生成物〔ｂ〕はｘ＝０．０５、生成物〔ｃ〕はｘ＝０．０７、生成物〔ｄ〕はｘ＝０．１、生成物〔ｑ〕はｘ＝０．０１、生成物〔ｒ〕はｘ＝０．０２の配合のものであり、生成物〔ｐ〕はｘ＝０、すなわち、ＳｒＣＯ3 およびＴｉＯ2 を用い、Ｒｈ2 Ｏ3 を用いず、Ｓｒ原子およびＴｉ原子のモル比がＳｒ:Ｔｉ＝１．０７:１となるよう配合したものである。
[Photocatalyst Preparation Examples a to d, p to r]
Rh-doped SrTiO 3 was synthesized by a solid phase method.
Specifically, a small amount of methanol (Kanto Chemical; 99, 8%) was used, SrCO 3 (manufactured by Kanto Chemical Co .; 99.9%), TiO 2 (manufactured by Soekawa Riken; 99.9%), Rh 2 O 3 (manufactured by Wako Pure Chemical Industries, Ltd.) has a molar ratio of Sr atom, Ti atom and Rh atom of Sr: Ti: Rh = 1.07: (1-x): x (x = 0 to 0.1) These were mixed in an alumina mortar. Subsequently, it pre-baked at 900 degreeC for 1 hour, and main baking was carried out at 1100 degreeC for 10 hours, and powdery product [a]-[d] and [p]-[r] were obtained.
The product [a] is x = 0.04, the product [b] is x = 0.05, the product [c] is x = 0.07, the product [d] is x = 0.1, The product [q] has a composition of x = 0.01, the product [r] has a composition of x = 0.02, and the product [p] has x = 0, that is, using SrCO 3 and TiO 2 , Rh 2 O 3 is not used, and the Sr atom and Ti atom molar ratio is Sr: Ti = 1.07: 1.
得られた粉末状の生成物〔ａ〕〜〔ｄ〕、〔ｐ〕〜〔ｒ〕を、それぞれ、Ｘ線回折装置「ＭｉｎｉＦｌｅｘ」（Ｒｉｇａｋｕ社製）を用いた粉末Ｘ線回折によってその結晶構造を調べたところ、生成物〔ｐ〕について、ＳｒＴｉＯ3 であることが同定され、生成物〔ａ〕〜〔ｄ〕、〔ｑ〕、〔ｒ〕については、いずれも、生成物〔ｐ〕と同様に、ほぼ単一相が合成されており、Ｒｈに由来の相が見られないことから、Ｒｈがその結晶格子中にドープされたＳｒＴｉＯ3 であると同定された。結果を図３に示す。
なお、図３において、（ａ）〜（ｄ）、（ｐ）〜（ｒ）は、それぞれ、粉末状の生成物〔ａ〕〜〔ｄ〕、〔ｐ〕〜〔ｒ〕についてのＸ線回折パターンを示す。
また、得られた粉末状の生成物〔ａ〕〜〔ｄ〕、〔ｑ〕、〔ｒ〕について、それぞれ、紫外−可視−近赤外拡散反射スペクトル（ＤＲＳ）を、紫外可視近赤外分光光度計「ＵｂｅｓｔＶ−５７０」（Ｊａｓｃｏ社製）を用いて測定し、得られた拡散反射スペクトルをＫｕｂｅｌｋａ−Ｍｕｎｋ法によって吸収モードに変換したところ、生成物〔ａ〕〜〔ｄ〕、〔ｑ〕、〔ｒ〕について、いずれも、可視光の吸収能を有することが確認された。これはドーパントであるＲｈによる新たな不純物準位の形成によるものだと推測される。
以下、粉末状の生成物〔ａ〕〜〔ｄ〕、〔ｐ〕〜〔ｒ〕を光触媒〔ａ〕〜〔ｄ〕、〔ｐ〕〜〔ｒ〕という。
The obtained powder products [a] to [d] and [p] to [r] are crystallized by powder X-ray diffraction using an X-ray diffractometer “MiniFlex” (manufactured by Rigaku), respectively. The product [p] was identified as SrTiO 3 , and the products [a] to [d], [q], and [r] were all the product [p] and Similarly, since almost a single phase was synthesized and no phase derived from Rh was found, Rh was identified as SrTiO 3 doped in its crystal lattice. The results are shown in FIG.
In FIG. 3, (a) to (d) and (p) to (r) are X-ray diffractions of powder products [a] to [d] and [p] to [r], respectively. Indicates a pattern.
Further, for the obtained powdery products [a] to [d], [q], and [r], ultraviolet-visible-near infrared diffuse reflectance spectra (DRS) are respectively obtained by ultraviolet-visible near-infrared spectroscopy. Measurement was performed using a photometer “UbestV-570” (manufactured by Jasco), and the obtained diffuse reflectance spectrum was converted into an absorption mode by the Kubelka-Munk method. The products [a] to [d], [q] [R] were confirmed to have a visible light absorption ability. This is presumably due to the formation of a new impurity level by the dopant Rh.
Hereinafter, the powder products [a] to [d] and [p] to [r] are referred to as photocatalysts [a] to [d] and [p] to [r].
〔光触媒電極の作製例ａ〜ｄ、ｐ〜ｒ〕
光触媒〔ａ〕〜〔ｄ〕、〔ｐ〕〜〔ｒ〕を用いて、光触媒電極を作製した。
具体的には、光触媒〔ａ〕２０ｍｇに、アセチルアセトン２０μＬを加え、さらに純水４０μＬを加えて混合することにより触媒ペーストを調製し、図１に従って、この触媒ペーストを、適当な大きさに切断したＩＴＯ透明電極（東京三容真空社製；７Ω／□）（２５）の導電面（２５Ａ）のメンディングテープ（住友スリーエム社製；厚さ５８μｍ）を枠状に貼り付けることによって区画した領域上に塗布した。次いで、大気中にて３００℃で２時間焼成処理をして光触媒部（２１）を形成した後、ＩＴＯ透明電極（２５）の導電面（２５Ａ）上の光触媒部（２１）を形成されていない部分にＧａ−Ｉｎ合金を塗布してオーミック接触部（２６）を形成し、そこに伸縮チューブ（２３）で被覆した銅線（２４）を銀ペースト（藤倉化成社製）で接着し、アラルダイト（登録商標）（昭和高分子社製）でＩＴＯ透明電極（２５）と銅線（２４）を接着し、最後に、光触媒部（２１）が形成されていないＩＴＯ透明電極（２５）の露出部分をアラルダイト（登録商標）で覆うことにより、光触媒電極〔ａ〕を得た。
光触媒〔ａ〕の代わりに光触媒〔ｂ〕〜〔ｄ〕、〔ｐ〕〜〔ｒ〕を用いたことの他は同様にして、光触媒電極〔ｂ〕〜〔ｄ〕、〔ｐ〕〜〔ｒ〕を得た。
[Photocatalyst electrode production examples a to d, p to r]
Photocatalyst electrodes were prepared using photocatalysts [a] to [d] and [p] to [r].
Specifically, a catalyst paste was prepared by adding 20 μL of acetylacetone to 20 mg of photocatalyst [a], and further adding 40 μL of pure water and mixing, and the catalyst paste was cut into an appropriate size according to FIG. On the area defined by sticking a moulding tape (Sumitomo 3M; thickness: 58 μm) on the conductive surface (25A) of ITO transparent electrode (Tokyo Sanyo Vacuum Co., Ltd .; 7Ω / □) (25) to a frame shape It was applied to. Subsequently, after baking in the atmosphere at 300 ° C. for 2 hours to form the photocatalyst part (21), the photocatalyst part (21) on the conductive surface (25A) of the ITO transparent electrode (25) is not formed. The part is coated with a Ga-In alloy to form an ohmic contact part (26), and a copper wire (24) covered with a telescopic tube (23) is adhered thereto with a silver paste (manufactured by Fujikura Kasei Co., Ltd.). The ITO transparent electrode (25) and copper wire (24) are bonded with registered trademark (made by Showa Polymer Co., Ltd.), and finally, the exposed portion of the ITO transparent electrode (25) where the photocatalyst portion (21) is not formed is removed. The photocatalytic electrode [a] was obtained by covering with Araldite (registered trademark).
Photocatalyst electrodes [b] to [d] and [p] to [r] are the same except that photocatalysts [b] to [d] and [p] to [r] are used instead of the photocatalyst [a]. ] Was obtained.
〔水素生成装置（３極式）の作製例ａ〜ｄ、ｐ〜ｒ：実施例１〜４、比較例１〜３〕
得られた光触媒電極〔ａ〕〜〔ｄ〕、〔ｐ〕〜〔ｒ〕を用いて、３極式の水素生成装置を作製した。
具体的には、図４に示されるように、イオン交換膜（１２）「Ｎａｆｉｏｎ（登録商標）Ｒ１１７」（ＤｕＰｏｎｔ社製）によってカソード室（１３Ａ）とアノード室（１３Ｂ）に仕切られた３電極型Ｈ型セル（１０）に、電解液（Ｗ）として０．１モル／ＬのＫ2 ＳＯ4 （関東化学社製；純度９９．０％）溶液を満たし、カソード室（１３Ａ）に光触媒電極〔ａ〕（１５）を設置すると共に、アノード室（１３Ｂ）に白金からなる対極（ＣＥ）（１７）を設置し、さらに、光触媒電極〔ａ〕（１５）を設置した室に参照極（１４）として飽和Ａｇ／ＡｇＣｌ電極（東亜ディーケーケー社製）を設置し、これらをそれぞれ電圧印加手段（１９）であるポテンショスタット「ＨＺ−５０００」（北斗電工社製）に、光触媒電極〔ａ〕（１５）を陰極、対極（１７）を陽極として電気的に接続することにより、水素生成装置〔ａ〕を作製した。
なお、白金からなる対極（１７）は、詳細には、白金板に白金線をスポット溶接により接続し、さらに白金線と銅線を接続し、白金板以外の部分を熱伸縮チューブで覆ったものである。
光触媒電極〔ａ〕の代わりに光触媒電極〔ｂ〕〜〔ｄ〕、〔ｐ〕〜〔ｒ〕を用いたことの他は同様にして、水素生成装置〔ｂ〕〜〔ｄ〕、〔ｐ〕〜〔ｒ〕を得た。
[Production Examples a to d, p to r of Hydrogen Generator (Tripolar Type): Examples 1 to 4, Comparative Examples 1 to 3]
Using the obtained photocatalytic electrodes [a] to [d] and [p] to [r], a tripolar hydrogen generator was produced.
Specifically, as shown in FIG. 4, three electrodes partitioned into a cathode chamber (13A) and an anode chamber (13B) by an ion exchange membrane (12) “Nafion (registered trademark) R117” (manufactured by DuPont). A type H-type cell (10) is filled with 0.1 mol / L K 2 SO 4 (manufactured by Kanto Chemical Co., Inc .; purity: 99.0%) as an electrolyte (W), and a photocatalytic electrode is filled in the cathode chamber (13A). [A] (15) is installed, a counter electrode (CE) (17) made of platinum is installed in the anode chamber (13B), and a reference electrode (14) is installed in the chamber in which the photocatalytic electrodes [a] (15) are installed. ), A saturated Ag / AgCl electrode (manufactured by Toa DK Corporation) was installed, and these were respectively connected to a potentiostat “HZ-5000” (made by Hokuto Denko) as a voltage application means (19), and a photocatalytic electrode [a] (15 ) Pole, the counter electrode (17) by electrically connecting the anode to prepare a hydrogen generator [a].
In addition, the counter electrode (17) made of platinum is, in detail, a platinum wire connected to a platinum plate by spot welding, further connecting a platinum wire and a copper wire, and a portion other than the platinum plate covered with a heat expansion tube. It is.
The hydrogen generators [b] to [d] and [p] are the same except that the photocatalyst electrodes [b] to [d] and [p] to [r] are used instead of the photocatalyst electrode [a]. To [r] were obtained.
〔水素生成装置（２極式）の作製例ｃＡ：実施例３Ａ〕
光触媒電極〔ｃ〕を用いて、２極式の水素生成装置を作製した。
具体的には、図２に従って、上記の水素生成装置（３極式）の作製例ａ〜ｄ、ｐ〜ｒにおいて、参照極を設けなかったことの他は同様にして、２極式の水素生成装置〔ｃＡ〕を作製した。
[Production Example cA of Hydrogen Generation Device (Bipolar Type): Example 3A]
Using the photocatalytic electrode [c], a bipolar hydrogen generator was produced.
Specifically, in accordance with FIG. 2, in the above hydrogen generation apparatus (3-pole type) production examples a to d and p to r, a bipolar electrode is similarly formed except that no reference electrode is provided. A generator [cA] was produced.
〔水素還元処理した光触媒に係る水素生成装置（２極式）の作製例ｃＢ：実施例３Ｂ〕
光触媒〔ｃ〕を石英管内に入れ、当該石英管内を水素ガスで置換した後に、加熱温度４００℃で５時間熱処理することにより水素還元処理を施した光触媒〔ｃＢ〕を得た。
光触媒電極の作製例ａにおいて、光触媒〔ａ〕の代わりに当該光触媒〔ｃＢ〕を用いると共に焼成処理を窒素気流中で行ったことの他は同様にして、光触媒電極〔ｃＢ〕を得、これを水素生成装置（２極式）の作製例ｃＡにおいて光触媒電極〔ｃ〕の代わりに用いたことの他は同様にして、２極式の水素生成装置〔ｃＢ〕を作製した。
[Production Example cB of Hydrogen Generation Device (Bipolar Type) Related to Photocatalyst Treated with Hydrogen Reduction: Example 3B]
The photocatalyst [c] was put in a quartz tube, and the quartz tube was replaced with hydrogen gas, followed by heat treatment at a heating temperature of 400 ° C. for 5 hours to obtain a photocatalyst [cB] subjected to hydrogen reduction treatment.
In photocatalyst electrode production example a, photocatalyst electrode [cB] was obtained in the same manner except that photocatalyst [cB] was used instead of photocatalyst [a] and the calcination treatment was performed in a nitrogen stream. Production Example of Hydrogen Generator (Bipolar) A bipolar hydrogen generator [cB] was produced in the same manner as in Example cA, except that it was used instead of the photocatalytic electrode [c].
以下の測定実験において、光の照射は、下記のように行った。
・紫外光を含む光の照射：３００Ｗのキセノンランプ（ＩＬＣ ｔｅｃｈｎｏｌｏｇｙ社製）からの光を、熱による寄与を抑えるために近赤外吸収フィルター「ＣＣＦ−５０Ｓ−５００Ｃ」（シグマ光機社製）によって近赤外光を吸収させ、Ｐｙｒｅｘ製ガラス装置を用いて３００ｎｍ以下の波長域の光を遮断し、球面平凸レンズ「ＳＬＳＱ−６０−１５０Ｐ」（シグマ光機社製）によって集光した光を、照射した。
・可視光の照射：３００Ｗのキセノンランプ（ＩＬＣ ｔｅｃｈｎｏｌｏｇｙ社製）からの光を、熱による寄与を抑えるために近赤外吸収フィルター「ＣＣＦ−５０Ｓ−５００Ｃ」（シグマ光機社製）によって近赤外光を吸収させ、カットオフフィルター（ＨＯＹＡ社製）によって４２０ｎｍ以下の波長域の光を遮断し、球面平凸レンズ「ＳＬＳＱ−６０−１５０Ｐ」（シグマ光機社製）によって集光した光を、照射した。
・太陽光の照射：ソーラーシュミレーター「ＰＥＣ−Ｌ１１」（Ｐｅｃｃｅｌｌ Ｔｅｃｈｎｏｌｏｇｉｅｓ製；１００ｍＷ／ｃｍ2 ）によって太陽光の照射を行った。
・光の照射は、いずれも、光触媒電極の光触媒の塗布面と反対の面に光が入射するように行った。
・光の照射を断続的に行う場合、そのＯＮとＯＦＦの切り替えは、モーターに半円型のステンレス板を取り付けた自作のチョッパーによって行った。
また、測定実験の前処理として、電解液中の溶存酸素を除く目的で撹拌子によって撹拌しながら１５分間窒素を用いてバブリングを行った。
In the following measurement experiments, light irradiation was performed as follows.
-Irradiation of light including ultraviolet light: Near-infrared absorption filter “CCF-50S-500C” (manufactured by Sigma Kogyo Co., Ltd.) to suppress the contribution of heat from a 300 W xenon lamp (manufactured by ILC technology). By absorbing near infrared light, blocking light in a wavelength region of 300 nm or less using a Pyrex glass device, and collecting light collected by a spherical plano-convex lens “SLSQ-60-150P” (manufactured by Sigma Koki Co., Ltd.). , Irradiated.
・ Visible light irradiation: Light from a 300 W xenon lamp (manufactured by ILC technology) is reduced to near red by a near-infrared absorption filter “CCF-50S-500C” (manufactured by Sigma Kogyo Co., Ltd.) to suppress the contribution of heat Absorbing external light, blocking light in a wavelength range of 420 nm or less by a cut-off filter (manufactured by HOYA), and collecting light collected by a spherical plano-convex lens “SLSQ-60-150P” (manufactured by Sigma Koki Co., Ltd.) Irradiated.
-Irradiation of sunlight: Irradiation of sunlight was performed with a solar simulator "PEC-L11" (Peccell Technologies; 100 mW / cm 2 ).
-Light irradiation was performed so that light was incident on the surface of the photocatalyst electrode opposite to the photocatalyst coating surface.
・ When light irradiation was performed intermittently, switching between ON and OFF was performed by a self-made chopper with a semicircular stainless steel plate attached to the motor.
Further, as a pretreatment for the measurement experiment, bubbling was performed using nitrogen for 15 minutes while stirring with a stir bar for the purpose of removing dissolved oxygen in the electrolytic solution.
＜Ｒｈのドープによる半導体特性の変化＞
Ｒｈがドープされた光触媒に係る水素生成装置〔ｂ〕、および、Ｒｈがドープされていない光触媒に係る水素生成装置〔ｐ〕をそれぞれ用い、紫外光を含む光を照射しながら掃引速度２０ｍＶ／ｓでＣＶ測定を行った。さらに、紫外光を含む光の代わりに可視光を照射しながら掃引速度２０ｍＶ／ｓでＣＶ測定を行った。結果を図５に示す。
なお、図５において、（ｂ−ＵＶ）、（ｂ−ＶＲ）は、水素生成装置〔ｂ〕について、それぞれ、紫外光を含む光、可視光の照射を行った場合のＣＶ曲線を示し、（ｐ−ＵＶ）、（ｐ−ＶＲ）は、水素生成装置〔ｐ〕について、それぞれ、紫外光を含む光、可視光の照射を行った場合のＣＶ曲線を示す。
<Change in semiconductor characteristics due to Rh doping>
Using a hydrogen generator [b] related to the photocatalyst doped with Rh and a hydrogen generator [p] related to the photocatalyst not doped with Rh, respectively, while sweeping light containing ultraviolet light, a sweep rate of 20 mV / s CV measurement was performed. Furthermore, CV measurement was performed at a sweep rate of 20 mV / s while irradiating visible light instead of light containing ultraviolet light. The results are shown in FIG.
In FIG. 5, (b-UV) and (b-VR) indicate CV curves when the hydrogen generator [b] is irradiated with light including ultraviolet light and visible light, respectively. (p-UV) and (p-VR) indicate CV curves when the hydrogen generator [p] is irradiated with light including ultraviolet light and visible light, respectively.
図５の結果から、水素生成装置〔ｐ〕、すなわちＲｈをドープしていない光触媒に係るものにおいては、アノード光電流が得られることから、ｎ型半導体特性を示すことが確認された。これに対して、水素生成装置〔ｂ〕、すなわちＲｈをドープした光触媒に係るものにおいては、カソード光電流が得られることから、ｐ型半導体特性を示すことが確認された。しかも、Ｒｈをドープした光触媒に係る水素生成装置〔ｂ〕においては、紫外光を含む光を照射したときのみならず、可視光を照射したときにもカソード光電流が得られることが確認された。 From the results shown in FIG. 5, it was confirmed that the hydrogen generator [p], that is, the photocatalyst not doped with Rh, exhibited an n-type semiconductor characteristic because an anode photocurrent was obtained. On the other hand, it was confirmed that the hydrogen generator [b], that is, the photocatalyst doped with Rh exhibits a p-type semiconductor characteristic because a cathode photocurrent is obtained. Moreover, in the hydrogen generator [b] relating to the photocatalyst doped with Rh, it was confirmed that the cathode photocurrent can be obtained not only when irradiated with light containing ultraviolet light but also when irradiated with visible light. .
＜Ｒｈのドープ量の変化による光応答性の変化＞
水素生成装置〔ａ〕〜〔ｄ〕、〔ｑ〕、〔ｒ〕をそれぞれ用い、可視光を照射しながら掃引速度２０ｍＶ／ｓでＣＶ測定を行った。結果を図６に示す。
なお、図６において、（ａ）〜（ｄ）、（ｑ）、（ｒ）は、それぞれ、水素生成装置〔ａ〕〜〔ｄ〕、〔ｑ〕、〔ｒ〕を用いた場合のＣＶ曲線を示す。
<Change in photoresponsiveness due to change in doping amount of Rh>
CV measurement was performed at a sweep rate of 20 mV / s using each of the hydrogen generators [a] to [d], [q], and [r] while irradiating visible light. The results are shown in FIG.
In FIG. 6, (a) to (d), (q), and (r) are CV curves obtained using the hydrogen generators [a] to [d], [q], and [r], respectively. Indicates.
図６の結果から、水素生成装置〔ａ〕〜〔ｄ〕、すなわちＲｈのドープ量が４〜１０モル％の光触媒に係るものにおいては、いずれも、カソード光電流が得られることから、ｐ型半導体特性を示すことが確認された。また、Ｒｈのドープ量が７モル％に達するまではそのドープ量が多くなるに従って得られるカソード光電流量が多くなり、７モル％の光触媒に係るものにおいて最大量のカソード光電流が得られ、１０モル％の光触媒に係るものにおいては７モル％の光触媒に係るものよりも得られるカソード光電流量が少なくなることが確認された。 From the results shown in FIG. 6, the hydrogen generators [a] to [d], that is, those relating to the photocatalyst having a Rh doping amount of 4 to 10 mol%, can obtain a cathode photocurrent. It was confirmed to show semiconductor characteristics. Further, until the doping amount of Rh reaches 7 mol%, the cathode photoelectric flow rate obtained increases as the doping amount increases, and the maximum amount of cathode photocurrent is obtained in the case of 7 mol% photocatalyst. It was confirmed that the cathode photoelectric flow rate obtained with the mol% photocatalyst was lower than that with the 7 mol% photocatalyst.
＜光の照射時間に対するカソード光電流量の変化＞
水素生成装置〔ｃ〕（光触媒電極の面積：３．１ｃｍ2 ）を用い、２５時間にわたって、参照極との間に−０．８Ｖの電位差を与えると共に、可視光を断続的に照射しながら定電位電解測定を行うと共に水素の生成量の測定を行った。定電位電解測定の結果を図７に示す。また、水素の生成量は２５時間で８２μｍｏｌであった。
<Change in cathode photoelectric flow rate with respect to light irradiation time>
Using a hydrogen generator [c] (photocatalytic electrode area: 3.1 cm 2 ), a potential difference of −0.8 V is applied to the reference electrode over 25 hours, and the light is intermittently irradiated with visible light. The potential electrolysis was measured and the amount of hydrogen produced was measured. The result of the constant potential electrolysis measurement is shown in FIG. The amount of hydrogen produced was 82 μmol in 25 hours.
図７の結果から、得られるカソード光電流量は、光の照射時間と共に徐々に増加することが確認された。また、水素の生成量は、得られるカソード光電流量に比例した量であった。このことから、得られたカソード光電流がＲｈの還元反応によるものではなく、水の還元反応によるものであることが判明した。 From the results of FIG. 7, it was confirmed that the obtained cathode photoelectric flow rate gradually increased with the irradiation time of light. The amount of hydrogen produced was proportional to the obtained cathode photoelectric flow rate. From this, it was found that the obtained cathode photocurrent was not caused by the reduction reaction of Rh but by the reduction reaction of water.
＜水素還元処理による光応答性の変化＞
水素還元処理を施していない光触媒による水素生成装置〔ｃＡ〕、および、水素還元処理を施した光触媒による水素生成装置〔ｃＢ〕をそれぞれ用い、可視光を照射しながら掃引速度２０ｍＶ／ｓでＣＶ測定を行った。結果を図８に示す。
なお、図８において、（ｃＡ）は水素還元処理していないものについてのＣＶ曲線、（ｃＢ）は水素還元処理したものについてのＣＶ曲線を示す。
<Change in photoresponsiveness due to hydrogen reduction>
CV measurement at a sweep rate of 20 mV / s while irradiating visible light using a hydrogen generator [cA] using a photocatalyst not subjected to hydrogen reduction treatment and a hydrogen generator [cB] using a photocatalyst subjected to hydrogen reduction treatment, respectively Went. The results are shown in FIG.
In FIG. 8, (cA) shows a CV curve for those not subjected to hydrogen reduction treatment, and (cB) shows a CV curve for those subjected to hydrogen reduction treatment.
図８の結果から、水素還元処理をした水素生成装置〔ｃＢ〕においては、水素還元処理をしない水素生成装置〔ｃＡ〕において得られるカソード光電流量の５倍量のカソード光電流が得られることが確認された。なお、水素還元処理によって、ＣＶ曲線におけるカソード光電流の立ち上がり位置が貴側にシフトしたことから、再結合中心の減少や新たな活性点の形成が示唆される。 From the result of FIG. 8, in the hydrogen generator [cB] subjected to the hydrogen reduction treatment, it is possible to obtain a cathode photocurrent that is five times the cathode photoelectric flow rate obtained in the hydrogen generator [cA] not subjected to the hydrogen reduction treatment. confirmed. The rising position of the cathode photocurrent in the CV curve shifted to the noble side by the hydrogen reduction treatment, suggesting that the number of recombination centers is reduced and a new active point is formed.
＜外部バイアスの大きさの変化によるカソード光電流量の変化＞
２極式の水素生成装置〔ｃＢ〕（光触媒電極の面積：１．１ｃｍ2 ）を用い、対極との間に、それぞれ０Ｖ（ノーバイアス）、−０．３Ｖ、−０．５Ｖ、−０．７Ｖ、−１．０Ｖの外部バイアスを印加すると共に可視光を断続的に照射しながら定電位電解測定を行った。結果を図９〜図１３に示す。
なお、図９〜図１３は、それぞれ、０Ｖ（ノーバイアス）、−０．３Ｖ、−０．５Ｖ、−０．７Ｖ、−１．０Ｖの外部バイアスを印加した場合の結果を示す。
<Change in cathode photoelectric flow rate due to change in external bias>
Using a bipolar hydrogen generator [cB] (photocatalytic electrode area: 1.1 cm 2 ), 0 V (no bias), −0.3 V, −0.5 V, −0. Constant potential electrolysis was performed while applying an external bias of 7 V and -1.0 V and irradiating visible light intermittently. The results are shown in FIGS.
9 to 13 show the results when external biases of 0 V (no bias), -0.3 V, -0.5 V, -0.7 V, and -1.0 V are applied, respectively.
図９〜図１３の結果から、いずれの大きさの外部バイアスの印加条件下においても、水の分解によるカソード光電流が得られることが確認された。すなわち、水の理論分解電圧（１．２３Ｖ）よりも小さい外部バイアスの印加条件下において、水の分解がなされることが判明した。 From the results of FIGS. 9 to 13, it was confirmed that the cathode photocurrent due to the decomposition of water can be obtained under any applied external bias condition. That is, it has been found that water is decomposed under the application of an external bias smaller than the theoretical water decomposition voltage (1.23 V).
＜光の照射時間に対する外部バイアスを印加しない条件下でのカソード光電流量の変化＞
２極式の水素生成装置〔ｃＢ〕と同様の構成を有し、その光触媒電極面積が１．４４ｃｍ2 である２極式の水素生成装置〔ｃＢ２〕を用い、２５時間にわたって、対極との間に外部バイアスを印加せず、可視光を断続的に照射しながら定電位電解測定を行った。結果を図１４に示す。
さらに、可視光の代わりに太陽光を断続的に照射しながら定電位電解測定を行った。結果を図１５に示す。
<Change in cathode photoelectric flow rate under the condition that no external bias is applied to the irradiation time of light>
Using a bipolar hydrogen generator [cB2] having the same configuration as that of the bipolar hydrogen generator [cB] and having a photocatalytic electrode area of 1.44 cm 2 , between the counter electrode for 25 hours. A constant potential electrolysis measurement was performed while intermittently irradiating visible light without applying an external bias. The results are shown in FIG.
Furthermore, constant potential electrolysis was performed while intermittently irradiating sunlight instead of visible light. The results are shown in FIG.
図１４の結果から、照射時間と共に得られるカソード光電流量が徐々に減少すること、および、光の照射がＯＦＦにされるｄａｒｋ時を経ることによって得られるカソード光電流量が回復することが確認された。
また、図１５の結果から、外部バイアスを印加せず、太陽光の照射の条件下においても、カソード光電流が得られることが確認された。このときの太陽エネルギーの変換効率は０．００３％であった。
From the results of FIG. 14, it was confirmed that the cathode photoelectric flow rate obtained with the irradiation time gradually decreased, and that the cathode photoelectric flow rate obtained through the dark time when the light irradiation was turned off was recovered. .
Further, from the results of FIG. 15, it was confirmed that a cathode photocurrent can be obtained even under the condition of sunlight irradiation without applying an external bias. The conversion efficiency of solar energy at this time was 0.003%.
以上の実施例および比較例の結果から、
・Ｒｈのドープ量が４〜１０モル％である光触媒による光触媒電極は、ｐ型半導体特性を示すこと。
・Ｒｈのドープ量に基づいて、７モル％をピークに、得られるカソード光電流量、すなわち水素生成量が増減すること。
・水素還元処理によってその水素生成能が向上すること。
・水の理論分解電圧（１．２３Ｖ）未満の外部バイアスの印加条件下において、水素を生成することができること。
・外部バイアスを印加しない条件下において、水素を生成することができること。
・可視光の照射下において、水素を生成することができること。
・太陽光の照射下において、水素を生成することができること。
が判明した。
From the results of the above examples and comparative examples,
-The photocatalyst electrode by the photocatalyst whose doping amount of Rh is 4-10 mol% shows p-type semiconductor characteristics.
-Based on the doping amount of Rh, the obtained cathode photoelectric flow rate, that is, the amount of hydrogen generation increases or decreases with a peak at 7 mol%.
・ Hydrogen generation ability is improved by hydrogen reduction treatment.
-Hydrogen can be generated under the application of an external bias less than the theoretical decomposition voltage of water (1.23 V).
-The ability to generate hydrogen under conditions where no external bias is applied.
-Able to generate hydrogen under visible light irradiation.
-The ability to generate hydrogen under sunlight.
There was found.
１０ セル
１２ イオン交換膜
１３Ａ カソード室
１３Ｂ アノード室
１４ 参照極
１５ 光触媒電極
１７ 対極
１９ 電圧印加手段
２１ 光触媒部
２３ 伸縮チューブ
２４ 銅線
２５ ＩＴＯ透明電極
２５Ａ 導電面
２６ オーミック接触部
Ｗ 電解液
Ｌ 光
DESCRIPTION OF SYMBOLS 10 Cell 12 Ion exchange membrane 13A Cathode chamber 13B Anode chamber 14 Reference electrode 15 Photocatalyst electrode 17 Counter electrode 19 Voltage application means 21 Photocatalyst part 23 Telescopic tube 24 Copper wire 25 ITO transparent electrode 25A Conductive surface 26 Ohmic contact part W Electrolyte L Light
Claims (7)
Ｒｈのドープ量が、当該ＳｒＴｉＯ 3 中においてＴｉ原子とＲｈ原子の合計を１００モル％としたときに、４〜１０モル％であり、ｐ型半導体特性を示すことを特徴とする光触媒電極。 Having a photocatalyst formed by doping Rh into Ti site of SrTiO 3 ;
Doping amount of Rh is, the sum of Ti atoms and Rh atoms is 100 mol% during the SrTiO 3, 4 to 10 mol%, the photocatalytic electrode, characterized in that indicating the p-type semiconductor characteristics.
前記光触媒電極と前記対極との間に外部バイアスを印加することなくまたは水の理論分解電圧未満の外部バイアスを印加すると共に、前記光触媒電極の光触媒に光を照射することにより、水が分解されて当該光触媒電極表面上に水素が生成されることを特徴とする水素生成装置。 The photocatalytic electrode according to any one of claims 1 to 3 and a counter electrode,
Water is decomposed by applying light to the photocatalyst of the photocatalyst electrode without applying an external bias between the photocatalyst electrode and the counter electrode or by applying an external bias lower than the theoretical decomposition voltage of water. A hydrogen generator, wherein hydrogen is generated on the surface of the photocatalyst electrode.
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